Kombucha is a kind of yeast, though some mistake it for a mushroom. The tea is made by fermenting tea with sugar and a culture of bacteria and yeast. It’s been consumed in China, Japan and Russia for at least the past 100 years as a health tonic, though it has only gained wide popularity in the U.S. in the past decade. It’s used as medicine for a laundry list of ailments, including memory loss, PMS, aging, AIDS, cancer, high blood pressure, immunity, metabolism, constipation, arthritis and hair regrowth. The science does not back up any of these claims. In fact, there are many documented side effects, including stomachaches, vomiting, nausea and headache. As a fermented food, it may stimulate digestion and provide probiotics, says Mary Purdy, RDN. The final word: If you want to try it, a safe choice is a pasteurized product from a brand you trust (but then you’ll miss out on the probiotics). For similar nutrients, get antioxidants from regular tea and probiotics from yogurt, kimchi or other fermented foods. The documented risks outweigh the potential benefits for those who are very young, very old, pregnant or whose immune systems are weakened.
Related: 7 Surprising Benefits of Fermented Foods